fix(background-agent): ignore metadata stream output

src/features/background-agent/session-stream-activity.test.ts

@@ -0,0 +1,41 @@
+import { describe, expect, test } from "bun:test"
+import {
+  hasOutputSignalFromPart,
+  resolveSessionNextPartInfo,
+} from "./session-stream-activity"
+
+describe("session.next stream activity", () => {
+  test("#given text delta event #when resolving part info #then it counts as output activity", () => {
+    // given
+    const timestamp = "2026-05-21T03:00:00.000Z"
+
+    // when
+    const partInfo = resolveSessionNextPartInfo("session.next.text.delta", {
+      sessionID: "ses-active",
+      timestamp,
+    })
+
+    // then
+    expect(partInfo?.type).toBe("text")
+    expect(partInfo?.field).toBe("text")
+    expect(partInfo?.activityTime).toEqual(new Date(timestamp))
+    expect(hasOutputSignalFromPart(partInfo, "ses-active")).toBe(true)
+  })
+
+  test("#given metadata stream event #when resolving part info #then it refreshes activity without counting as output", () => {
+    // given
+    const timestamp = "2026-05-21T03:00:00.000Z"
+
+    // when
+    const partInfo = resolveSessionNextPartInfo("session.next.compaction.started", {
+      sessionID: "ses-active",
+      timestamp,
+    })
+
+    // then
+    expect(partInfo?.type).toBeUndefined()
+    expect(partInfo?.field).toBeUndefined()
+    expect(partInfo?.activityTime).toEqual(new Date(timestamp))
+    expect(hasOutputSignalFromPart(partInfo, "ses-active")).toBe(false)
+  })
+})